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            <div><h3 class="title">
                <a name="asio.tutorial.tuttimer1"></a><a class="link" href="tuttimer1.html"
                                                         title="Timer.1 - Using a timer synchronously">Timer.1 - Using a
                timer synchronously</a>
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    <p>
        This tutorial program introduces asio by showing how to perform a blocking
        wait on a timer.
    </p>
    <p>
        We start by including the necessary header files.
    </p>
    <p>
        All of the asio classes can be used by simply including the <code class="computeroutput"><span class="string">"asio.hpp"</span></code>
        header file.
    </p>
    <pre class="programlisting"><span class="special">#</span><span class="identifier">include</span> <span
            class="special">&lt;</span><span class="identifier">iostream</span><span class="special">&gt;</span>
<span class="special">#</span><span class="identifier">include</span> <span class="special">&lt;</span><span
                class="identifier">asio</span><span class="special">.</span><span class="identifier">hpp</span><span
                class="special">&gt;</span>
</pre>
    <p>
        All programs that use asio need to have at least one I/O execution context,
        such as an <a class="link" href="../reference/io_context.html" title="io_context">io_context</a> or
        <a class="link" href="../reference/thread_pool.html" title="thread_pool">thread_pool</a> object. An
        I/O execution context provides access to I/O functionality. We declare an
        object of type <a class="link" href="../reference/io_context.html" title="io_context">io_context</a>
        first thing in the main function.
    </p>
    <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">main</span><span
            class="special">()</span>
<span class="special">{</span>
  <span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_context</span> <span
                class="identifier">io</span><span class="special">;</span>
</pre>
    <p>
        Next we declare an object of type asio::steady_timer. The core asio classes
        that provide I/O functionality (or as in this case timer functionality) always
        take a reference to an io_context as their first constructor argument. The
        second argument to the constructor sets the timer to expire 5 seconds from
        now.
    </p>
    <pre class="programlisting">  <span class="identifier">asio</span><span class="special">::</span><span
            class="identifier">steady_timer</span> <span class="identifier">t</span><span class="special">(</span><span
            class="identifier">io</span><span class="special">,</span> <span class="identifier">asio</span><span
            class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span
            class="identifier">seconds</span><span class="special">(</span><span class="number">5</span><span
            class="special">));</span>
</pre>
    <p>
        In this simple example we perform a blocking wait on the timer. That is,
        the call to <a class="link" href="../reference/basic_waitable_timer/wait.html"
                       title="basic_waitable_timer::wait">steady_timer::wait()</a>
        will not return until the timer has expired, 5 seconds after it was created
        (i.e. not from when the wait starts).
    </p>
    <p>
        A timer is always in one of two states: "expired" or "not
        expired". If the <a class="link" href="../reference/basic_waitable_timer/wait.html"
                            title="basic_waitable_timer::wait">steady_timer::wait()</a>
        function is called on an expired timer, it will return immediately.
    </p>
    <pre class="programlisting">  <span class="identifier">t</span><span class="special">.</span><span
            class="identifier">wait</span><span class="special">();</span>
</pre>
    <p>
        Finally we print the obligatory <code class="computeroutput"><span class="string">"Hello,
        world!"</span></code> message to show when the timer has expired.
    </p>
    <pre class="programlisting">  <span class="identifier">std</span><span class="special">::</span><span
            class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span
            class="string">"Hello, world!"</span> <span class="special">&lt;&lt;</span> <span
            class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span
            class="special">;</span>

  <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
<span class="special">}</span>
</pre>
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        See the <a class="link" href="tuttimer1/src.html" title="Source listing for Timer.1">full source listing</a>
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        Return to the <a class="link" href="../tutorial.html" title="Tutorial">tutorial index</a>
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    <p>
        Next: <a class="link" href="tuttimer2.html" title="Timer.2 - Using a timer asynchronously">Timer.2 - Using a
        timer asynchronously</a>
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            <div class="copyright-footer">Copyright © 2003-2022 Christopher M. Kohlhoff<p>
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